The present invention relates generally to integrated circuit devices, and more specifically to integrated circuit devices which may be used in applications having different input voltage thresholds.
There often exists a need to have multiple input voltage thresholds on integrated circuit devices. Integrated circuit devices which may benefit from having multiple input voltage threshold capabilities include memories, logic devices such as PLDs (Programmable Logic Devices), processors such as microprocessors, and gate arrays such as ASICs (Application Specific Integrated Circuits). Such integrated circuit devices may require multiple input voltage threshold capabilities if there exists one or more logic families, such as TTL (Transistor-Transistor Logic) and CMOS (Complementary Metal Oxide Semiconductor), or if it is desirable to maintain voltage levels when switching between voltage standards, such as 5 volts and 3.3 volts.
For many integrated circuit devices, such as microprocessors, there exists two different voltage standards: 5 volts and 3.3 volts. Input voltage levels high, V.sub.IH, and low, V.sub.IL, may be defined the same for both voltage standards. For example, the low input voltage level V.sub.IL is 0.8 volts while the high input voltage level V.sub.IH is 2.2 volts for TTL compatible voltage levels. In addition to TTL compatible levels, CMOS compatible levels may also employ multiple voltage standards. Like TTL, CMOS compatible logic levels also have a V.sub.IL and a V.sub.IH well known in the art. Thus, it is often desirable to be able to have multiple input voltage thresholds. For example, it would be desirable for an integrated circuit device to be CMOS compatible and TTL compatible at 5 volts, as well as to be CMOS compatible and TTL compatible at 3.3 volts.
Currently, multiple input thresholds for an integrated circuit device are provided by making costly changes to a metal mask of the device. Metal mask changes are costly and time consuming to implement. Therefore, there is a current need in the art for an integrated circuit device to be able to respond to various input voltage thresholds or power supply voltage conditions by making only minimal changes to the integrated circuit device.